An Application-Specific Integrated Circuit (ASIC) is a microchip designed for a special application. The ASIC is designed to process information or complete tasks in a manner specific to the intended application. For example, ASICs are used in such diverse applications as auto emission control, environmental monitoring, and personal digital assistants (PDAs). ASICs are contrasted with general integrated circuits that can be used to perform different tasks for different applications. Examples of general integrated circuits include the microprocessor and the random access memory chips in a typical personal computer.
An ASIC can be mass-produced for a special application or can be custom manufactured for a particular customer application. Custom production is typically performed using components from a “building block” library of ASIC components. Each ASIC includes a number of input/output (I/O) leads that allow the ASIC to be connected to a larger circuit and receive the signals and data with which the ASIC works. These I/O leads are typically arranged in an array known as a Land Grid Array (LGA). The ASIC is usually attached to a circuit board, such as a printed circuit board (PCB). Leads or a socket on the circuit board make contact with the I/O leads of the LGA and connect the ASIC to the larger circuit of which it is a part.
The ever growing I/O count in today's large ASICs requires a very high clamping load to secure the ASIC to the circuit board and ensure continuous electrical contact between the ASIC and the circuit on the PCB. Clamping loads in the range of 400 to 700 pounds are becoming common. As noted, a socket may be provided on the PCB into which the ASIC is clamped.
The load necessary to secure the ASIC to the PCB is produced by the hardware used to attach the ASIC to the circuit board. This hardware is frequently referred to as the “attach hardware.” The attach hardware includes a bolster plate and a load plate. The load plate is a rigid plate that is typically made of steel and is sometimes referred to as a spring plate. The bolster plate is similar.
The ASIC assembly is sandwiched between the load plate and the bolster plate. Load studs connect the load plate and bolster plate, and a load screw is tightened to push the load plate and bolster plate apart causing the load plate to flex and generate the desired clamping force to the ASIC and circuit board.
Because the clamping load required is so high, the force can cause the PCB and/or the bolster plate to bow or deflect. This will impede the operation and performance of the socket or other connection between the ASIC and the PCB. Consequently, the bow of the bolster plate must be minimized. In some applications, this requires minimizing the load applied. On the other hand, the socket or connection between the ASIC and PCB requires a certain minimum load to be reliable. The result is that the load is constrained from above and below. The load must be sufficient to provide a reliable connection in the socket or between the ASIC and PCB, but must not be strong enough to cause a significant bow in the bolster plate or circuit board. Consequently, the load range must be minimized.
Previous designs have attempted to minimize load range by providing a hard stop for the load screw that limits the load that can be applied. In other instances, torque settings or measurements are taken to insure the load screw is operated within a narrow load range.